Control Systems

An Overview of Control Systems and MCUS

- By Stuart Ball

Control systems make up a substantial percentage of all embedded systems and there are many varieties that fall within the broad category. Stuart takes us on a brief tour of control systems, explaining the differences and discussing which are best suited for specific applications and why the differences matter.

Control systems are how the real world is controlled by an MCU. In this article, I'll focus on what a control system is and how it works. I've touched on some of these concepts in previous columns, so I'll be repeating but summarizing some of the same information here. This article won't turn you into a controls engineer, but it will give you an understanding of what control systems are and what they do. I'll focus on embedded control systems here. And I'll leave out the calculus.

FIGURE 1 Mechanical speed governor

WHAT IS A CONTROL SYSTEM?

A control system is a way to maintain some device at a specific temperature, speed, pressure, or something similar. A control system may turn things on or off in response to some external signal. Control systems can be mechanical or electrical; in the "olden" days, mechanical governors were used to control the speed of steam and diesel engines. Figure 1 shows a very simplified example; a pair of hinged weights are attached to a drive shaft that is driven from the engine, which drives the drive wheel either through a belt or gearing. As the speed goes up, centrifugal force causes the weights to move away from the center, closing a throttle valve (not shown) and decreasing the speed. If the speed is too low, the weights move closer to the center, opening the valve and increasing the speed.